A simulation-based evaluation of two proposed alternatives to Luer devices for use in neuraxial anaesthesia


  • Presented in part at the Association of Anaesthetists of Great Britain & Ireland Annual Congress, Harrogate, September 2010

Correspondence to: Dr Tim Cook
Email: timcook007@googlemail.com


The National Patient Safety Agency has issued a Patient Safety Alert with the aim of eliminating Luer connectors from equipment for lumbar puncture and subarachnoid injections by 1 April 2011, and from all neuraxial and regional anaesthesia equipment in 2013. B-link (UK) Ltd and InterVene Ltd have produced non-Luer connectors for neuraxial devices: the Neurax® and Spinalok® respectively. Using an adult spinal simulator, 59 experienced clinicians performed neuraxial procedures using these devices and reported on specific performance characteristics and overall usability. Cross-connectivity between non-Luer and Luer connectors was also examined. The median (IQR [range]) overall assessment scores (0–10 scale) of usability for the standard, Neurax and Spinalok systems were 8 (8–9 [7–10]), 6 (5–7 [0–8]) and 7 (6–8 [1–9]) for spinal procedures and 8 (8–9 [6–10]), 7 (5–8 [1–9]) and 4 (3–6 [0–9]) for epidural procedures, respectively. Both study systems scored significantly lower than standard equipment for overall performance of spinal and epidural procedures, although the performance of non-Luer devices was mostly rated ‘adequate’ or better. Both non-Luer connectors could cross-connect with one or more Luer connectors. Following feedback to the manufacturers, both systems have been modified and cross-connectivity apparently has been eliminated. Our results indicate that clinicians may not find non-Luer devices immediately ‘user-friendly’. More importantly, some cross-connectivity with Luer devices was possible. Our findings illustrate that introducing equipment that is fully compliant with the National Patient Safety Agency alert poses a significant challenge to manufacturers and clinicians. We conclude that before introducing any non-Luer device into widespread use, independent, formal evaluation should be carried out.

Luer connectors enable fluid and drug administration devices (such as syringes, fluid lines, catheters and needles) to connect to each other. Their use in multiple administration routes creates the potential for wrong-route neuraxial administration (that is, a drug intended for the intrathecal or epidural space accidently administered intravascularly or vice versa) that may lead to patient harm or death [1–3]. The ongoing problem is illustrated by 11 cases of wrong-route neuraxial drug administration reported to the Third National Audit Project of the Royal College of Anaesthetists (NAP3) [4]. This included one fatality due to accidental intravenous administration of a large volume of bupivacaine [5]. The National Reporting Learning System continues to receive regular reports of wrong-route errors in anaesthesia [6], and there have been at least two fatalities from such events in the last 5 years in the UK [5, 7]. Several other medical specialities also access the central neuraxis for diagnostic and therapeutic purposes. At least 55 cases of intrathecal injection of vinca alkaloids, intended for intravenous use, have been reported worldwide [8], invariably leading to paralysis or death. The National Patient Safety Agency (NPSA) continues to identify wrong-route drug administration as a concern during intrathecal chemotherapy [9], and elimination of harm from this cause was one of four specific targets in the Department of Health’s report An Organisation with a Memory, published in 2006 [10].

In 2004, the NPSA recommended that non-Luer compliant connectors should be used for all neuraxial procedures and that new designs should be tested before introduction [11]. In 2006, three prototypes were examined, but only one successfully completed laboratory, simulation and clinical assessment stages [12–14]. The elimination of wrong-route errors by redesign of connectors was endorsed by the Health Select Committee in 2009. In November 2009, the NPSA issued a Patient Safety Alert stating that ‘from 1 April 2011 all spinal (intrathecal) bolus doses and lumbar puncture samples should be performed using syringes, needles and other devices with connectors that will not also connect with intravenous equipment’ [15]. This directive extends to all neuraxial and regional anaesthesia equipment in 2013 [16]. User testing of this newly developed equipment is logical before a wholesale changeover takes place in 2011; indeed, this is advocated in NPSA documentation [6].

In this manikin-based study of simulated neuraxial procedures, we evaluated the usability of two alternatives to Luer connectors for neuraxial devices, comparing each with standard equipment currently in clinical use in our hospital. The devices chosen were the only two available at the time the study commenced. The study was based on methods and protocols developed and used for earlier Department of Health and NPSA funded evaluations of non-Luer neuraxial connectors [13].


The study outline was submitted to the local Research Ethics Committee (Royal United Hospital, Bath, UK) which deemed that ethical approval was not required. Fifty-nine clinicians from the Royal United Hospital Bath, who perform neuraxial procedures in their routine practice, were recruited to participate in this study. Clinicians included anaesthetists, oncologists/haematologists, paediatricians and physicians with a range of relevant skills and experience. All participation was voluntary and each participant gave written consent.

Four clinical simulations were performed on an anatomically realistic adult spinal trainer manikin (Lifeform® Spinal Injection Simulator; Simulaids, Coalville, UK). ‘Standard equipment’ was selected by determining, for each procedure, what was routinely used for that procedure in the host hospital. For spinal anaesthesia, a 25-G Whitacre needle with introducer (Vygon, Cirencester, UK) and 3-ml Luer-lock syringe (Becton Dickinson, Madrid, Spain) were used. For epidural injection, a 16-G Tuohy needle, loss-of-resistance syringe (Luer-slip connector), 16-G epidural catheter and filter (Luer-lock connector) and a 10-ml Luer-slip injection syringe (all Smiths Medical, Hythe, Kent, UK) were used. For intrathecal chemotherapy and lumbar puncture, a 22-G Quincke needle with introducer (BBraun, Melsungen, Germany) and a 10- and 5-ml Luer-slip syringe were used. As lumbar puncture and intrathecal chemotherapy injection used the same equipment and small numbers of participants were recruited, data from these evaluations were combined for analysis. All single-use equipment was used only once.

B-link (UK) Ltd (Shipley, UK) and InterVene Ltd (Chesterfield, UK) have produced non-Luer connectors for neuraxial devices: the Neurax® and Spinalok® respectively. The Neurax system retains the same polarity as the Luer system (a proximal male connector inserts into a distal female connector) and includes both slip and lock connectors (Fig. 1). The connector differs from the Luer system in both the taper and diameter of its cone. The Spinalok system has reverse polarity and also has slip and lock connectors (Fig. 2). Study devices were supplied by the two participating manufacturers. For each clinical simulation, the manufacturer was asked to supply equipment corresponding to that described above with appropriate non-Luer connectors. In some cases, needles or catheters of a different gauge were supplied; the Spinalok® epidural set included a 9-cm needle and 18-G catheter.

Figure 1.

 The Neurax® slip connector in close up view. Top: collared locking connector on the spinal syringe; bottom: ‘slip connector’.

Figure 2.

 The Spinalok® connector in close up view. Top: ‘slip connector’; bottom: locking connector.

Before each procedure, clinicians were taught how to use the new equipment by one of the investigators. All procedures were performed with gloves to enhance realism in the simulated scenarios, but simulated sterilisation and a full sterile technique were not used. Where possible, the sessions were video-recorded. Participants were instructed to perform the procedure safely and in the time and manner they would usually practise. Each clinician performed the simulated neuraxial procedure first using the standard equipment, gaining familiarity with the manikin and aiding comparison with study devices. The procedure was then repeated for each study system. The order of use of non-Luer devices was determined randomly using two opaque face-down cards, the first one chosen by the participant indicating the first device to evaluate.

Data were collected via structured interviews and by observation. Participants rated the standard equipment and two study systems on a 5-point modified Likert scale (1: very difficult/very poor; 2: less than acceptable; 3: acceptable; 4: good; 5: very easy/very good) for appearance, handling, ease of attaching a syringe and needle, connection security, cerebrospinal fluid visibility through the hub, ease of injecting and robustness of the equipment. For epidural systems, the ease of introducing a catheter through the needle and attaching the catheter adapter and filter were also evaluated. Participants were asked to provide feedback regarding perceived strengths and limitations of each system, to choose which of the two new systems they preferred, and to suggest any changes required before introducing it into clinical practice. Overall usability was reported using a 11-point scale from 0 (totally unacceptable) to 10 (excellent). The participants were also asked to determine whether the test devices could ‘cross-connect’ with Luer devices when used in a manner that might arise clinically (either in combinations that are designed to occur or in unexpected but feasible combinations). Using the device in a manner that was outwith the manufacturer’s instructions, but that might arise by error, was acceptable. Participants were not allowed to alter the equipment or make connections that were very clearly not ones that might reasonably be made by human error. For cross-connectivity testing, a random selection of Luer equipment (available from our hospital’s routinely used equipment) was used; this included several syringes with Luer-slip and -lock connectors, intravenous cannulae and a three-way tap.

Statistical analysis was performed with spss 16.0 (SPSS Inc., Chicago, IL, USA). Each study system was compared with the standard equipment using the Wilcoxon signed-rank test. Differences were considered significant when p < 0.05.


The results of the usability assessment are summarised in Table 1.

Table 1.   Clinician-reported evaluations of performance of standard equipment and two non-Luer neuraxial devices, the Neurax® and Spinalok®, for spinal and epidural anaesthesia and lumbar puncture/chemotherapy, on a manikin. All assessments were made using a modified Likert scale (1: very difficult/very poor; 2: less than acceptable; 3: acceptable; 4: good; 5: very easy/very good) except overall usability, which was rated using a 0–10 scale. Values are median (IQR [range]) or number.
  Spinal (= 25) Epidural (= 25)Lumbar puncture and chemotherapy (= 19)
  1. CSF, cerebrospinal fluid.

  2. *p < 0.05 compared with the standard equipment.

  3. †p < 0.01 compared with the standard equipment.

Appearance of equipment4 (4–5 [3–5])3 (3–4 [2–4])†4 (4–5 [3–5])5 (4–5 [3–5])3 (3–4 [2–5])†3(3–4 [2–5])†4 (3–4 [3–5])4 (3–5 [2–5])4 (3–4 [1–5])
Handling of equipment for procedure5 (4–5 [4–5])3 (3–4 [2–4])†3 (3–4 [1–5])†5 (4–5 [3–5])4 (3–4 [2–5])†3 (2–3 [2–4])†4 (4–5 [3–5])4 (2–4 [2–5])*4 (2–4 [2–5])*
Attaching syringe and needle4 (4–5 [2–5])2 (2–3 [1–4])†4 (3–4.5 [1–5])*5 (4–5 [3–5])4 (3–4 [2–5])†3 (2.5–4 [1–5])†4 (3–4 [2–5])3 (3–4 [2–5])4 (3–4 [3–5])
Connection security4 (4–5 [2–5])3 (2–4 [1–5])†4 (3–5 [2–5])4 (3–4 [2–5])4 (3–5 [1–5])2 (2–3 [1–4])†3 (3–3 [2–4])3 (2–4 [1–5])4 (3–4 [2–5])*
CSF visibility through hub4 (3.5–4 [3–5])3 (2.5–4 [1–5])†4 (3.5–5 [1–5])   4 (3–4 [2–5])4 (3–4 [2–5])4 (2–5 [2–5])
Ease of injecting5 (4–5 [3–5])3 (3–5 [1–5])†4 (3.5–4.5 [2–5])†4 (4–5 [3–5])4 (3–4.5 [1–5])*3 (2.5–4 [1–5])†4 (3–5 [3–5])4 (3–5 [1–5])4 (4–5 [3–5])
Ease of disconnecting syringe from needle4 (4–5 [2–5])3 (3–4 [1–5])†4 (3–4 [2–5])4 (4–5 [3–5])3 (3–4 [2–5])†4 (3–4 [2–5])†4 (4–5 [3–5])4 (3–5 [2–5])4 (4–5 [3–5])
Introducing catheter through the needle   4 (4–5 [3–5])4 (3–4 [2–5])*3 (2–4 [1–5])†   
Attaching catheter adaptor and filter   4 (3–5 [3–5])4 [3.5–4 (1–5)]2 (2–3 [0–4])†   
Perceived robustness of equipment4 (4–5 [3–5])3 (3–3 [1–4])*3 (2–4 [1–4])†4 (4–5 [2–5])4 (3–4 [1–5])*2 (2–3 [1–5])†4 (3–4 [3–5])3 (2–4 [1–5])4 (2–4 [2–5])
Overall usability8 (8–9 [7–10])6 (5–7 [0–8])*7 (6–8 [1–9])†8 (8–9 [6–10])7 (5–8 [1–9])†4 (3–6 [0–9])†7 (6–8 [5–9])6 (4–8 [0–10])7 (5–8 [3–10])
Preferred system 619 214 118

Spinal simulation

Twenty-five anaesthetists participated. The standard system was rated as good or better (≥ 4/5) for all aspects of usability.

In all measures of performance, the Neurax system was rated significantly poorer than the standard system (Table 1). Despite this, majority of median scores differed from the standard system by only one point and all the medians for the Neurax system were ‘adequate’ except for ‘attaching syringe and needle’ which was rated as ‘less than acceptable’. Ten participants reported leakage at the connector interface with the Neurax system when injecting and several experienced difficulty with securing connection without displacing the needle from the subarachnoid space. The presence of the collar on the Neurax syringe led to adverse comments by nine who considered it ‘confusing’. Disconnection while performing aspiration was reported by three participants. One participant rated overall usability as 0 due to repeated difficulties with securing the connection between the needle and the syringe; disconnection occurred whenever aspiration was attempted and the procedure was abandoned.

For four measures of usability, there was no difference between the Spinalok and the standard system. In four measures and in overall assessment of usability, the Spinalok system was rated significantly poorer. The median assessment of usability was ‘adequate’ in two measures and ‘good’ in six. There were no reports of leakage, disconnection or displacement during aspiration. Difficulty with aspiration was reported by six participants due to perceived stiffness of the syringe.

Nineteen participants preferred the Spinalok system and six, the Neurax system.

Epidural simulation

Twenty-five anaesthetists participated. The standard system was rated as ‘good’ or better for all aspects of usability.

For two measures of usability, there was no difference between the Neurax and standard systems. In six measures and in overall assessment, the Neurax system was rated significantly poorer. The median assessment of usability was ‘adequate’ in two measures and ‘good’ in seven. Four participants reported leakage and eight expressed concern due to difficulties with connection and disconnection.

For all measures of usability and in overall assessment, the Spinalok system was rated significantly poorer than standard equipment. The median assessment of usability was ‘less than adequate’ in three measures, ‘adequate’ in five and ‘good’ in one. The security of the connection for the epidural filter, rather than the connection between the needle and the syringe, led to several poor scores. Some users expressed concern that epidural filter disconnection may occur and two participants scored the system 0 overall on this basis. No leakage was reported.

Twenty-one participants preferred the Neurax system and four the Spinalok system.

Lumbar puncture and intrathecal chemotherapy simulation

A total of 19 clinicians (oncologists/haematologists, paediatricians and physicians) participated, all of whom regularly perform the procedure they were evaluating. The standard system was rated as ‘good’ for all aspects of usability except for connection security (rated as ‘adequate’).

There were no significant differences between the median scores for the Neurax and standard systems, except for handling of equipment in which Neurax scored less well. The median assessment of usability was ‘adequate’ in three measures and ‘good’ in five. Leakage was reported by six participants, although four felt that there was less leakage with the Neurax system than the standard kit. In one batch of spinal needles, a manufacturing fault led to poor anchoring of the needle within the hub and needle protrusion inside the hub: this participant scored the system as 0.

There was no significant difference between the median scores for the Spinalok and the standard systems, except for ‘connection security’ in which Spinalok scored better and handling of equipment in which it scored less well. The median assessments were ‘good’ in all measures. There were no reports of leakage.

Eleven participants preferred the Neurax system and eight, the Spinalok system.


Several participants found it possible to connect a BD Luer Plastipak syringe (Luer-slip and -lock) (Becton Dickinson) to the female component of the Neurax system. This connection was noted only with the Neurax Tuohy needle and epidural filter (Fig. 3). Although only ∼3 mm of the syringe nozzle entered the Neurax connector, the connection was leak-free. This occurred only when a significant axial force and torque were applied. Subsequent investigations suggested that this force approached 70 N. The connection appeared to occur due to a combination of deformation of the relatively soft BD syringe nozzle and subsequent deformation of the Neurax connector once a connection had occurred: the syringe more easily entered other new Neurax connectors, and new syringes connected more easily with a Neurax connector after it had been ‘breached’ for the first time. Several other makes of Luer-slip syringe that appeared to be made from harder plastic, (for example, a Portex epidural loss-of-resistance syringe) could not be connected to the Neurax connector.

Figure 3.

 Cross-connection of BD syringe male Luer connector into a female connector of a Neurax® epidural needle.

The male needle connector of the Spinalok system was found to connect retrogradely to the male component of a BBraun Discofix three-way tap (BBraun, Melsungen, Germany) (Fig. 4). In this connection, the external component of the male Spinalok connector entered the inside of the male Luer connector. Once attached, the connection was leak-free. Several other male Luer connectors were tested without connection being noted (the BBraun Discofix three-way tap is made of thin rigid plastic and has an unusually large internal diameter).

Figure 4.

 Cross-connection of a BBraun three-way Luer tap with a Spinalok® male connector.

Additional comments

In each evaluation, specific comments on each device’s strengths and weaknesses were sought. These were summarised (see Appendix) and the manufacturers were informed.


There are two aspects to our results. First, we have assessed the usability (clinician acceptability) of two new non-Luer systems of neuraxial equipment. In direct comparison with the standard systems, the new devices were rated less good overall, but in absolute terms, the new devices generally scored as ‘acceptable’. Second, we have assessed the potential for cross-connectivity and found to our surprise that both new systems can be made to cross-connect with Luer connectors.

As indicated above, there is more than one interpretation of our results, which might lead to the conclusion that the new connectors are ‘not acceptable’ (relatively less acceptable than standard systems) or that they are ‘acceptable’ (rated as adequate overall). Although care was taken to prevent potential bias against the new systems (at the beginning of each session, all participants were updated on the NPSA alert regarding the replacement of Luer equipment with non-Luer systems, and they were asked to evaluate each new system objectively and critically on the basis of its performance only), it must be acknowledged that aspects of study design may bias against the new systems. The standard equipment in each evaluation was that routinely used in our hospital, and for reasons of choice and familiarity, it is likely that this will evaluate well. In contrast, the new systems were unfamiliar to the participants and their use required slight modification of the clinicians’ technique. Dislike of change, lack of confidence with a new device and even general disapproval of the need for non-Luer connectors may all have biased against the new systems, and this is likely to be reflected in the narrow ranges and high scores quoted for the overall usability of the ‘standard’ equipment. The new devices were also delivered by manufacturers as soon as available and while not prototypes, this led to more than one episode where equipment needed to be returned to the manufacturer as there was a problem with either the manufacturing process or construction; data from these evaluations were excluded and the evaluations repeated before analysis. Despite this, it is notable that the wide ranges found in the overall usability scores for both the Spinalok and the Neurax systems suggest a great diversity of opinion amongst clinicians. When trusts are considering purchasing such equipment, it may therefore be prudent to canvass opinion amongst local clinicians formally, to ascertain preferences.

Leakage with the Neurax system was reported by a minority of participants, a problem that has not been prominent in previous reports of earlier Neurax systems. It is possible this was a training issue rather than a mechanical issue; the device requires a rather firmer ‘push-to-fit’ than the Luer connector.

Although we did not perform direct comparisons between the two non-Luer systems (our interest was in comparing each device with the current standard rather than against each other), it is notable that the Spinalok system performed better than the Neurax system for spinal anaesthesia, but for epidural anaesthesia, the opposite was true, and for lumbar puncture and chemotherapy, both devices performed similarly. User preference confirmed these observations and user comments regarding system limitations are helpful in understanding these results (see Appendix). The rotating collar on the 3-ml Neurax syringe was considered bulky, and contributed to problems creating a leak-free connection. This difficulty is consistent with studies of previous versions of the Neurax system [13, 14]. Difficulties identified with the Spinalok system mostly related to the spinal needle stylet and epidural filter connectors. The Spinalok epidural system was supplied with an 18-G, 9-cm needle, and this may have also influenced evaluation compared with the shorter and wider-bore standard system.

There are several interpretations of our finding of differential preferences. First, it could indicate that our results are inconsistent and therefore unreliable. Second, as the participants in each part of the evaluation differed (although with much overlap between spinal and epidural groups), the results might indicate differences in clinicians’ subjective opinions. Third, it is possible that the participants were influenced in their evaluations by differences in design of the various needles, syringes and other system components, rather than just the connectors. Ideally, we would have evaluated identical systems, differing only in the type of connector, but commercial alliances mean that a certain connector will be attached to a certain syringe, needle etc. Last, we observed that each of the procedures performed is subtly different. For example, fine spinal needles are often held by participants very gently between two fingers and advanced with a very low force and delicate finger movements. In contrast, placement of a larger epidural needle and attachment of filters etc. appears to be a more forceful procedure with more use of larger muscle groups – the wrists and forearms. Thus, different systems may actually suit the different procedures differently.

In some respects, the cross-connectivity results are our most concerning findings. The primary aim of introducing non-Luer connectors is to eliminate the possibility of delivering intravenous drugs to the neuraxis and vice versa; cross-connectivity with standard Luer connectors means that this aim is not achieved with certainty. Both manufacturers were understandably concerned at our findings. It is useful to discuss the two systems separately.

The Neurax system has been evaluated in various forms on several occasions before and cross-connectivity has not been identified as a clinically relevant problem. It appears that there was an element of serendipity in that the syringes we chose to use to test cross-connectivity are made of rather soft plastic; stiffer syringes will not connect. The force required to connect a male Luer syringe to the female Neurax needle was estimated, using a force gauge provided by the manufacturers, to be about 70 N. We consider this certainly more than would usually be applied during spinal procedures and probably more than would be used during the siting of an epidural. Participants made the cross-connection only with the epidural needle and epidural filter despite all connectors' being made of identical material. This may be because the shape of the epidural needle and filter allows a firmer grip to be made, or may illustrate how different motor movements and forces are used for the different clinical procedures. After some discussion, we considered this cross-connectivity to be clinically relevant, as inexperience or poorly taught clinicians or other staff (such as those changing epidural infusions) might make such a connection without recognising it as erroneous. We also found it possible to inject fluid contained in a Neurax syringe through a three-way tap, but the connection was so obviously wrong (leakage exceeding 50% of fluid, connection completely unstable and inability to inject with 1 cmH2O of back pressure) that we did not consider it a clinical risk.

The Spinalok system was found to connect to a three-way tap. For this connection, the male component of the Spinalok system was inserted into the inside of the male component of the Luer connector. Again, there was a degree of chance as the particular BBraun three-way tap we used is made of rather rigid plastic and as a result, the manufacturers have been able to reduce the internal diameter of the male Luer. Importantly, although the external diameter of the Luer connector is defined in the relevant ISO standard, this is not so for the internal diameter. It should be noted that this BBraun male Luer has been assessed independently using Luer test gauges, and was found to comply with the ISO standard (P. Philips, Surgical Material Testing Laboratory, Bridgend, Wales, personal communication). We tried several other types of three-way tap and other male Luer components, none of which connected to the Spinalok system. Once connected, the three-way tap would enable connection of any Luer syringe and thus the possibility of erroneous injection. Discussions with the manufacturer centred on whether this finding was of any clinical relevance. The manufacturers highlighted the statement in the NPSA Safety Alert, under ‘recommended actions’, that trusts should ‘eliminate the use of three-way taps, and adaptors with Luer connectors, which enable connection of specified devices to intravenous devices’. They argued that three-way taps should never be found, therefore, where neuraxial procedures are performed and only mis-use could lead to a problem. Our opinion was that this was a limited interpretation of the document, based on an interpretation of the statement with which we did not agree. We firmly believe that the elimination of all three-way taps from medical practice is impractical and that a latent risk would therefore remain. In addition, the fact that the cross-connection was found on a three-way tap was not a specific finding, and a similar ‘large bore’ Luer used in another medical device could lead to cross-connection.

Our findings illustrate that the simple engineering challenge of producing a Luer-incompatible system is not as easy as might be expected. To prevent a connection to the female Luer, the obvious change is to make the new non-Luer male connector larger; however, by doing this, the female non-Luer component will also be larger, leading to the possibility of cross-connection with the (smaller) male Luer. Of course, the reverse process also applies. More imaginative solutions (such as those of B-link and InterVene) are needed, but each has potential problems. Most of the devices used in this evaluation were CE-marked and the others were pre-production devices. It might be expected that CE-marked devices designed to be incompatible with Luer connectors would, by definition, not have the problems we identified. However, the CE marking process has never been a guarantee of clinical performance or even that a device is fit for purpose [17]. This may be considered by some to be a failing of the CE process itself.

The identified cross-connections were discussed at some length with each manufacturer. As a result of these constructive discussions, both non-Luer systems have been promptly revised and we briefly discuss the revisions here. The internal diameter of the female component of the Neurax system was reduced by 0.1 mm and then 0.2 mm. The first change meant that only by using a very high force (which frequently broke the syringe nozzle) could a Luer syringe be attached. A majority of anaesthetists, when shown this system, stated that it did not cross-connect. The second change made cross-connection so difficult that all who tried it rejected it as ‘not possible’ (Fig. 5). The external diameter of the male pin in the Spinalok system* was enlarged until its external diameter exceeded the minimum diameter allowable for a male Luer connector, according to the ISO standard. This theoretically makes it physically impossible to connect an un-deformed Spinalok male connector to a male Luer connector that meets ISO standards (Fig. 6). Provisional tests confirmed lack of cross-connectivity. We have not performed re-testing of either of the revised systems in terms of usability or testing of complete systems for cross-connectivity, and the above comments should be interpreted with that in mind.

Figure 5.

 Failure of attempted cross-connection of a BD syringe male Luer connector into a revised female Neurax® connector.

Figure 6.

 Failure of attempted cross-connection of a B-Braun three-way Luer tap with a revised Spinalok® (Surety®) male connector.

This study has several limitations. First, it was performed on a manikin in a single unit; however, in assessing the new connectors, we are examining an engineering solution to a clinical problem and the numerous advantages of simulation (speed, consistency, affordability, absence of ethical issues) make it a very suitable first step for evaluation. Second, the evaluations rely on some subjective assessment and the results suggest that clinicians were influenced in their responses by more than just the connectors. Communications with manufacturers have included comments that our evaluation does not have adequate rigour and that it lacks standards against which manufacturers might judge their equipment. This has some validity; formal laboratory tests such as those under development for the proposed ISO standard for small bore connectors (such as the use of fixed axial and torque forces needed to connect and disconnect, and assessment of liquid and air leakage) might usefully be performed to establish standards that must be reached before clinical evaluation is justified. However, we emphasise that the main aim of this study was to assess the usability and clinical acceptability of non-Luer neuraxial connectors, by performing simulated clinical procedures similar to those likely to be performed in real clinical practice. There is no robust evidence that compliance with objective measures of performance (standards) in this field will lead to more acceptable or better products, and there are significant limitations to laboratory testing of devices designed to be used for clinical procedures requiring fine motor skills and sensitive sensory feedback. Laboratory testing should, perhaps, be seen as providing a minimum level of performance that devices should attain before being assessed clinically, therefore complementing rather than replacing usability testing. Third, our assessment of cross-connectivity used only a small sample of Luer devices and failure to cross-connect would not have excluded such a problem. However, we did identify cross-connectivity issues with both test connectors. Finally, we did not correct for multiple statistical testing (to do so would reduce the risk of false positives, but increase the risk of false negatives). We recognise that there is a risk of false positive results, but considered it more important to detect any possible differences between the devices and standard equipment, than it was to avoid false negatives.

It would be easy to criticise the two manufacturers involved in this evaluation as both test systems had limitations, including cross-connectivity. We believe this would be wrong. The engineering solution to this problem is not as easy as many clinicians (and perhaps politicians) may consider. Both manufacturers submitted their equipment to full independent evaluation, were flexible about the tests we performed, provided samples as rapidly as feasible and responded promptly to all issues raised during the evaluation. In that respect, they are unique amongst manufacturers, to date. Following communication of identified problems, the manufacturers were pro-active in addressing these rapidly and rigorously. Initial informal evaluations of both revised devices suggest that the identified cross-connectivity problems have been satisfactorily resolved. This process required careful communication between researchers and manufacturers, allied with considerable trust. The process of independent evaluation, feedback and revision of devices again makes the two manufacturer’s products unique amongst currently available equipment. As we have not performed full evaluation of the revised devices, we cannot completely confirm non-connectivity, or whether the changes have altered usability characteristics.

The NPSA’s Patient Safety alert has created a deadline for introduction of alternatives to Luer connectors. This has some clear advantages and has, at last, brought progress towards a solution where previously there was considerable inertia. However, there are dangers associated with the use of such a deadline: if not managed appropriately, there is a risk of new unintended and perhaps unpredicted risks, both of which might lead to patient harm. The introduction of single-use tonsillectomy surgical equipment is an example of a safety-based change in practice that led to unintended consequences [18, 19]. It is important to note that the NPSA guidance does include the option, where clinicians or an organisation deems appropriate, of not changing to non-Luer devices at the time of the deadline, provided the continued use of Luer devices is then placed on the trust’s risk register [6].

We conclude that issues of usability and safety of new non-Luer devices are likely to be identified only by independent evaluation. We propose that all such non-Luer devices are subjected to independent evaluation before purchase or clinical use. Such evaluation would ideally involve laboratory evaluation against benchmark standards, an investigation of cross-connectivity with Luer devices and clinicians’ evaluation of usability. This is a considerable challenge for manufacturers, clinicians and regulatory authorities that will be achieved only through co-operation.


  • *

    the revised version renamed Surety®

Acknowledgements and competing interests

Dr Tim Cook represents the Royal College of Anaesthetists on the NPSA Safer Neuraxial Devices External Reference Group. The views expressed in this article do not represent those of the Royal College of Anaesthetists, the NPSA or the Safer Neuraxial Devices External Reference Group. The evaluations reported here were performed with equipment provided by the relevant manufacturers or distributors. These companies took no further part in the evaluation process. The manufacturers have been shown a draft of this report for correction of factual errors only. The project was supported by grants from the Research and Development Department of Royal United Hospital NHS Trust Bath and from the NPSA. We thank all clinicians involved in the project, and the manufacturers for the supply of equipment and prompt responses to all issues raised.


Clinicians’ comments from evaluation of standard equipment and two non-Luer neuraxial devices, the Neurax® and Spinalok®, for spinal and epidural anaesthesia and lumbar puncture/chemotherapy, on a manikin. Comments are included when provided by at least three participants (number provided in brackets).

ProcedureSystem limitationSystem strengths
  1. CSF, cerebrospinal fluid.

Standard kit
 SpinalNeedle displaces when locking the system (4)Familiar system (15)
Simple, easy to use, good quality, robust kit (5)
Good and secure Luer lock (4)
 EpiduralConnecting catheter to filter fiddly, becomes disconnected (4)Robust, well-made, easy-to-use kit (12)
Familiar (9)
Good loss-of-resistance syringe (6)
 Lumbar puncture and intrathecal chemotherapy Easy to use, simple (4)
 SpinalStylet loose, flimsy and wobbly – difficult to refit (12)
Loose, not secure connection, leakage, no feedback that the system is securely connected (10)
Syringe collar confusing, makes connector bulky (9)
Not easy to observe CSF through the coloured hub (8)
Fiddly connection may displace the needle (6)
Connection becomes loose when aspirating (3)
Labelled syringe/yellow colour (10)
Good size and shape of introducer needle hub (7)
Good CSF visibility (4)
Spinal needle rigid and comfortable to hold (4)
Looks similar to the standard kit and feels familiar (4)
 EpiduralHave to push hard to engage the connector; needle may be displaced and disconnecting the system not easy (8)Similar to the standard kit; the same catheter, filter connector, needle graduation (13)
Stylet removal not smooth – can pull the needle out and bends on introducing (5)Good connector design: simple, obvious, no leak (7)
Distracting multiple colours (5)Yellow colour on syringe/syringe labelled as Neurax (6)
Loose, not secure connector, leakage (4)Good kit; easy to use, simple, robust (6)
Metal stylet (3)Solid, robust stylet (4)
Difficulty introducing catheter through the needle – needs catheter introducer (3)Good quality loss-of-resistance syringe (3)
Filter cannot be flushed on its own; bonded filter connection (3) 
 Lumbar puncture and intrathecal chemotherapyLeakage (7)
Have to apply extra force to secure connection (3)
Stylet does not fit the needle hub snugly (3)
Secure connection (4)
Good needle hub design; large hub, easy to hold, good grip (4)
Ease of connecting and disconnecting (3)
Similar to standard (3)
Good CSF visibility through hub (3)
 SpinalBad quality stylet; wobbly, loose, not attached to needle – falls out when inserting, very difficult to re-introduce back into needle (20)Good CSF visibility through hub (15)
Nice spinal needle hub design; comfortable to hold, good grip (13)
Difficulty with observing CSF through lengthy needle hub, particularly when aspirating (10)Syringe connection; good lock, easy to use (9)
Good looking, elegant kit (6)
Longer spinal needle (8)Yellow colour on syringe (5)
Difficulty with aspirating due to stiff syringe (6)Introducer and needle as one assembly (3)
Spinal needle feels flexible, bendy and not rigid (6) 
Connection felt not secure (5) 
Unfamiliar design (4) 
 EpiduralPoor design of filter connector; too long, cumbersome, time consuming and confusing to assemble, too many loose parts, danger of disconnecting (21)
Needle longer than standard (17)
Poor stylet quality; flimsy and wobbly, difficult to re-introduce into needle, doesn’t fit the needle hub snugly, falls out spontaneously (14)
Difficult to introduce catheter into needle due to too small needle hub diameter, needs catheter introducer (9)
Confusing catheter graduation (6)
Connector not intuitive to use (5)
Loss-of-resistance syringe too loose (4)
Loss-of-resistance syringe as good as standard plus has yellow plunger (5)
Longer needle (3)
Attaching catheter easy (3)
 Lumbar puncture and intrathecal chemotherapyLoose stylet connection to needle hub – falls out spontaneously (10)
Difficulty with re-inserting stylet into needle due to very small needle hub diameter (6)
Poor CSF visibility through Quincke needle hub (4)
CSF gets collected into needle hub space (4)
Wobbly stylet, difficult to re-insert back into needle (3)
Good and secure connection (7)
Nice needle hub size and shape (3)
Good CSF visibility through needle hub (3)
As good as standard kit (3)